Antiphospholipid (aPL) antibodies are autoantibodies which can be detected in plasma or serum in solid phase immunoassays employing negatively charged phospholipids, most commonly cardiolipin (CL) as the antigen.
A simple 2-step procedure for purifying aPL antibodies from plasma (or serum) using sequential phospholipid affinity and cation-exchange chromatography, yielding specific immunoglobulin of &gt;95% purity has been described. These antibodies exhibit typical binding in CL-ELISA but do not possess lupus anticoagulant (LA) activity in phospholipid dependent clotting tests. Recently, it has also been shown that plasma can be resolved by ion-exchange chromatography into fractions containing either anticardiolipin (aCL) antibodies or antibodies with LA activity, strongly suggesting that aCL and LA antibodies represent distinct aPL antibody subgroups, and appear to be directed against a different antigen.
Solid phase immunoassays to detect plasma or serum antibodies which bind phospholipid antigens (such as cardiolipin [CL]) were developed in the mid 1980's and are now available as ready to use Commercial kits, from a number of Biotechnology companies as commercial kits, and many laboratories use these, or alternatively use their own `in house` assays. Essentially CL is coated onto the bottom of microtitre wells and serum or plasma samples added. Anticardiolipin, aPL antibodies are bound which can be detected using enzyme-linked anti-human (second) antibodies. It has been noted however, that some samples exhibit binding lower than predicted when diluted and the explanation for this is unclear. However, this gives rise the problem that some samples may be `falsely` negative because of a dilution effect. Anti-phospholipid antibodies (aPL) detected in solid phase enzyme linked immunoassays (ELISA) employing cardiolipin (CL) as the antigert are termed anticardiolipin antibodies (aCL). aCL have been detected in patients with syphilis and other infections, in autoimmune disease, as a drug induced condition and in a percentage of the normal population.
The presence of aCL in patients with autoimmune disease confers an increased risk of arterial and venous thrombosis, recurrent spontaneous foetal loss and thrombocytopaenia. However, these clinical features are not associated with aCL occurring in syphilis or other infections.
This suggests that there is some qualitative difference between aCL found in the two groups. Thus there is a need for a method for determining whether antiphospholipid antibodies in a sample are antibodies to an autoimmune disease or antibodies to an infectious disease as well as for a method for determining whether antiphospholipid antibodies to an autoimmune disease and antiphospholipid antibodies to an infectious disease are present in a sample.